Magnesium oxide (MgO) plays an important role in optical glass, and its purity directly affects the optical, mechanical and chemical stability of the glass. The following discusses the impact of magnesium oxide purity on optical glass from multiple aspects:
1. Definition of magnesium oxide purity
The purity of magnesium oxide usually refers to the content of its main component MgO, which is generally expressed as mass percentage (%). The purity requirements for magnesium oxide for optical glasses are usually above 99.9%, and even high-end applications are required.
99.99% (grade 4N) or higher (grade 5N).
Impurity ingredients include:
Metal impurities (such as Fe, Al, Ca, Si, Na, etc.) – affect the light transmittance, refractive index and dispersion of glass.
Non-metallic impurities (such as C, S, Cl, etc.) – affect the chemical stability and optical uniformity of glass.
2. The influence of purity on optical properties
(1) Light transmittance and impurity absorption
High purity MgO helps reduce the absorption of impurities in the glass and makes the light transmittance higher.
Metal impurities such as Fe²⁺ and Fe³⁺ will cause the absorption of visible and ultraviolet light, causing color deviations in the glass.
When SiO₂ and Al₂O₃ are excessive, it may affect the optical uniformity of the glass.
(2) Stability of refractive index
Low-purity magnesium oxide may bring in other metal oxides, affecting the uniformity of refractive index of optical glass.
High purity MgO can ensure that the refractive index meets the design requirements and improve the accuracy of the optical system.
(3) Color and optical uniformity
Low-purity magnesium oxide may cause yellowing of glass or uneven color spots, affecting the imaging quality of high-precision optical instruments.
The higher the purity, the closer the color of the glass is to be transparent and colorless, and is suitable for high-end optical devices such as telescopes, microscopes and laser lenses.
3. Effect of purity on mechanical and thermal properties
(1) Heat resistance of glass
High purity MgO can improve the heat resistance of optical glass and maintain stable optical properties under high temperature environments.
Impurities (such as alkali metal oxides such as Na and K) may reduce the softening point of the glass and affect the service life of the glass under high temperature conditions.
(2) Mechanical strength of glass
High purity MgO can improve the hardness and impact resistance of glass, making it more suitable for high-precision optical systems.
Low purity MgO may lead to uneven stress distribution in the glass and reduce durability.
4. Effect of purity on chemical stability
High purity MgO can improve the acid, alkali and moisture resistance of glass, so that it can maintain stable performance in harsh environments.
Impurities (such as carbonates, sulfates, etc.) may reduce the corrosion resistance of glass, resulting in deterioration of the surface of the optical element.